This application is based upon and claims benefit of priority of Japanese Patent Application No. 2002-217885 filed on Jul. 26, 2002, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electronic control unit mounted on a supporting bracket by snap-fitting and a structure for snap-fitting the electronic control unit to the supporting bracket.
2. Description of Related Art
A conventional structure for mounting an electronic control unit for use in an automotive vehicle on a supporting bracket will be described with reference to FIGS. 6-11 attached hereto. As shown in FIG. 6, an electronic control unit 1 having a case 40 mounted on a bracket 20 is fixed to a stay 10 positioned in an inside space of an instrument panel. The bracket 20 is connected to a pair of angled supports 30a, 30b which are fixed to the stay 10 by screws 300a, 300b. 
As shown in FIG. 7, the case 40 is box-shaped and has a front opening 41, through which a circuit board 60 carrying electronic components thereon is inserted or taken out. A connector 61 is mounted on the circuit board 60 at its front end. After the circuit board 60 is inserted into the case 40, the front opening 41 is covered with a front cover 50. As shown in FIG. 8, the case 40 includes a rear wall 42 positioned opposite to the front opening 41 and sidewalls 43, 44. A rear projection 42a is formed on the rear wall 42, a pair of side projections 43a, 43b are formed on the sidewall 43, and another pair of side projections 44a, 44b are formed on the other sidewall 44. Each projection has a rectangular plane surface and is projected from the respective wall by a certain height.
The bracket 20 is made of an iron plate, and includes a bottom wall 21, a resilient rear hook 22 and four resilient side hooks 23-26 as shown in FIG. 9. Each hook is bent upwardly form the bottom wall 21, and its angle relative to the bottom wall 21 can be resiliently widened when the case 40 is mounted on the bracket 20. The resilient rear hook 22 has a hole 220 that engages with the rear projection 42a formed on the rear wall 42 of the case 40. Similarly, the resilient side hooks 23-26 have respective holes 230-260 that engage with the side projections 43a, 43b, 44a, 44b, respectively.
Referring to FIGS. 10 and 11, a process for mounting the case 40 on the bracket 20 will be described. The circuit board 60 is inserted into the case 40, and the opening 41 is closed with the front cover 50. As shown in FIG. 10, the case 40 is placed on the bracket 20, so that the rear projection 42a faces the resilient rear hook 22, and side projections 43a, 43b, 44a, 44b face the resilient side hooks 23, 24, 25, 26, respectively. Then, the case 40 is forcibly pushed toward the bottom wall 21 of the bracket 20 to resiliently widen the respective hooks. As shown in FIG. 11, the case 40 has to be also pushed toward the resilient rear hook 22 against its resilient force. Thus, all the projections formed on the case 40 are snap-fitted to the holes 220-260 formed in the respective resilient hooks 22-26 of the bracket 20. In this manner, the case 40 is fixedly mounted on the bracket 20.
However, in the conventional mounting structure described above, the case 40 is pushed back by the spring-back force of the resilient rear hook 22. Therefore, the side projections may not be correctly aligned with the respective resilient side hooks. In this case, the projections do not engage with the resilient hooks. To correctly position the case 40 relative to the bracket 20, it is conceivable to provide an additional projection on the front cover 50 and another hook that engages with the additional projection on the bracket 20. However, such is not practical because the circuit board 60 cannot be taken out from the case 40 after the case 40 is mounted on the bracket 20 if the front cover 50 is connected to the bracket 20.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved electronic control unit that can be easily and firmly snap-fitted to a bracket. Another object of the present invention is to provide an improved structure for snap-fitting the electronic control unit to the bracket.
An electronic control unit includes a box-shaped case and a circuit board on which various electronic components are mounted. The circuit board is inserted into the case from a front opening of the case, and the front opening is closed with a front cover after the circuit board is inserted. The electronic control unit is mounted on a bracket by snap-fitting projections of the case to resilient hooks of the bracket. A rear projection is formed on a rear wall of the case and a pair of side projections is formed on each sidewall of the case. The case is made of a resin material, and all the projections are integrally formed with the case. The bracket is made of an iron plate, and the resilient hooks stand upwardly from a bottom wall of the bracket. A guiding projection is also formed on at least one of the sidewalls of the case. When the case is mounted on the bracket, the guiding wall guides the case to align the projections with the respective resilient hooks with which the projections engage.
To mount the case on the bracket, the case is placed on the bracket so that projections roughly align with the respective resilient hooks. The case is further pushed down toward the bracket, resiliently widening the resilient hooks, to thereby allow the projections to engage with the hooks. At the same time, the case is pushed toward the rear side against a resilient force of the rear hook by a thrusting force of the guiding projection. Preferably, a sloped surface slidably contacting one of the resilient hooks is formed on the guiding projection to effectively generate the thrusting force. In this manner, all the projections of the case are aligned with and snap-fitted to the respective resilient hooks by simply pushing down the case toward the bracket. Thus, the electronic control unit is easily mounted on the bracket without fail.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.